6as7g powered OTL headphone amps

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kominak

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Joined 2006
#1
Hello,
a couple of years ago I've got a pair of GEC 6as7g tubes for cheap and I'd like to put them to some good use now. I want to build an OTL tube headphone amp to drive my Beyerdynamic DT880 (600ohm version). So far I've found these projects:

Peter Millett's HA-2
Van Waarde OTL headphone amp project from headwize
BottleHead Crack and Crackatwoa (kit)
Singlepower Extreme (known to have issues)

.. are there any others?

Could any of the owners please chime in to help me decide which one to build?

I'm currently leaning towards the HA-2, because:
1. given the high DT880 impedance a single 6as7g should be enough (no need for SinglePower extreme dual output tubes)
2. I have a chassis that I can use (no need to pay for Crack chassis and tubes + expensive shipping and customs fees to EU)
3.I have a couple of Mullard GZ34 rectifiers that are begging to be used (I realize I'll have to deal with slightly higher voltage over 5u4)

But if it's expected to gain some sonic benefits from Crack/Crackatwoa (or any other) over HA-2, I'm willing to try that one instead.

I will use my AMB Gamma2 dac as a source. Soundwise I prefer clean over colored sound, don't need much bass, the detailed midrange and soundstage is much more important to me.

Thanks a lot for the input...
Martin
 
#2
I only have the Crack with Speedball mod here and the 6AS7G tube is one of my favorites.Its a simple circuit, its absolutely quiet, very musical and with my high impedance T90's its a stellar performer.

I looked at some of the others in your list and did not like the higher background noise or hiss mentioned in some reviews.

Good luck!
Alex
 
#3
There is also the Chinese made Darkvoice 336.

I have built a number of Bottlehead Cracks as its a very good amplifier, low noise floor, low distortion, and a very good frequency response. If you want that "warm and tubey" sound you wont find it, all of Bottleheads amps are very clean and detailed sounding.

I cant find schematics for those other options, but i would put my money on a Crack+Speedball being superior as the speedball adds constant current sources for the 12au7 and 6080 tubes, and the 12au7 is LED biased. The Crackatwoa is the same audio circuit with a shunt regulated power supply. I've not heard one of those so i cant comment on the differences.
 
#6
Schematics:

Ha-2: http://www.pmillett.com/wheatfield/manual.pdf

Van Waarde: the original page on HeadWize was taken down, but similar project with slightly altered power supply is here: 6AS7 Headphone Amplifier (schematics on the bottom of the page)

BottleHead Crack: it's easy to read the circuit from the gut shots of the amplifier - very similar to Van Waarde, but uses Ecc82 instead of ecc88 as driver tube which is biased using red led diode instead of resistor. Speedball is C4S constant current source I believe. Both Crack and Speedball are easier(and possibly cheaper) to just order from BottleHead than trying to source all the parts.

SinglePower Extreme: http://gilmore.chem.northwestern.edu/singlehourextreme.jpg

I hope I didn't violate any owner's rights by posting these links. If yes, moderators please take appropriate action and I apologize in advance.

Martin
 
#8
We discussed a 6as7g based headphones amp a while back here : http://www.diyaudio.com/forums/tube...dphone-project-ec88-6080-a-8.html#post3834514
Click to expand...

Thanks for the link, it was good and informative read.

It's much cheaper (almost 1/2) to source your own parts for the crack and the speedball when you're in Europe. Much less convenient though.
Click to expand...
It turned out you were right about the cost - after searching through my spare parts bin I found out I'm only missing some $30 worth of parts. 150V transformer, tubes, chassis and ALPS pot are all gathering dust in the attic...
 
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